Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM® Corporation. The MR sensor transduces magnetic field changes in an MR stripe to resistance changes, which are processed to provide digital signals. Data storage density can be increased because an MR sensor offers signal levels higher than those available from conventional inductive read heads for a given bit area. Moreover, the MR sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity. In operation the magnetic storage medium, such as tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto.
The quantity of data stored on a magnetic tape may be increased by increasing the number of data tracks across the tape. More tracks are made possible by reducing feature sizes of the read and write elements, such as by using thin-film fabrication techniques and MR sensors. In modern magnetic tape recorders adapted for computer data storage, read-while-write capability with MR sensors is an essential feature for providing fully recoverable magnetically stored data. The interleaved R/W magnetic tape head with MR, GMR, AMR, TMJ, etc. sensors allows increased track density on the tape medium while providing bi-directional read-while-write operation of the tape medium to give immediate read back verification of data just written onto the tape medium. A read-while-write head assembly includes, for each of one or more data tracks, a write element in-line with a read element, herein denominated a R/W pair, wherein the gap of the read element is closely-disposed to and aligned with the gap of the write element, with the read element positioned downstream of the write element in the direction of medium motion. By continually reading just-recorded data, the integrity of the recorded data is immediately verified while the original data is still available in temporary storage in the recording system. The recovered data is compared to the original data to afford opportunity for action, such as re-recording, to correct errors. The interleaved head contains two opposed modules, each of which contains interleaved R/W tracks. Alternate columns (track-pairs) are thereby disposed to read-after-write in alternate directions of tape medium motion. Tape heads suitable for reading and writing on high-density tapes also require precise alignment of the track-pair elements in the head assembly.
FIG. 1 illustrates a piggyback head module 100 which can also function as a portion of a read-while-write head. As shown, the head includes several R/W pairs 102 in a “piggyback” configuration. As with the interleaved heads, servo readers 104, which are not piggybacked, are positioned on the outside of the array of R/W pairs 102. The servo readers 104 follow servo tracks for the particular data “band” of the tape being read or written to, their signal being used to keep the head aligned within the band. The tape may have a single or many data bands, and each band may have one or more servo tracks. Typically, the servo tracks separate the data bands, and both servo readers in the head read servo data simultaneously for accurate positioning.
When the head is constructed, layers are formed on a substrate 110 in generally the following order for the R/W pairs 102: an insulating layer 112, a first shield (S1) 114, a sensor 116 also known as a read element, a second shield (S2) 118, and first and second writer pole tips (P1, P2) 120,122.
Of significance, note that writers are not formed over the shields surrounding the servo reader 104 since writers are not needed at these locations. Also of significance, note that in the interleaved head the servo readers and data readers are similar in form to the piggyback head servo readers.
Tape heads in particular suffer from head wear caused by motion of the magnetic recording tape. Repeated passes of the tape medium over the wear-resistant tape head surface may eventually selectively wear away the portion of the surface containing the read/write elements, which can impair head performance. This is a particular problem for thin-film magnetic heads where the thin-film layers may see relatively considerable wear with brief operation, giving an unacceptably rapid loss of signal for the magnetic head assembly. Practitioners in the art may provide wear-resistant layers on the air bearing surfaces of magnetic heads to inhibit wear, for example, a sputtered layer of diamond-like carbon or aluminum oxide, but such layers are also very thin, being perhaps 20 nanometers thick to minimize tape-to-head spacing loss, and must generally be deposited onto pre-recessed heads.
A particular wear problem is selective to the servo readers of piggyback heads and the servo and data readers of interleaved heads, which have been found to recess more than piggybacked data readers. This additional recession is disadvantageous for head-assembly life-expectancy. That the piggyback data readers experience less recession is believed to be due to the proximity of the more wear-resistant writer poles.
Another problem encountered with bare reader heads is that the read sensors are susceptible to failure due to shield-shorting as a result of running magnetic recording tape thereacross at very low humidity, which is found to produce accumulations of conductive material on the MR element and shields. The only known solution is to forcibly recess the sensor, so that its components do not develop the conductive accumulation. Such a recessed sensor has been implemented but is difficult to manufacture, and also results in an undesirable spacing loss for the data readers, which must read much higher frequencies than the servo readers.
Data and servo readers in the interleaved head are similar to the servo reader in the piggybacked head in regards to susceptibility to excess erosion and low humidity shorting with very smooth media
There is accordingly a clearly-felt need in the art for a wear-resistant read/write head assembly having servo readers with improved wear characteristics and improved reliability. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.